Drum sieves



Aug. 19, 196 9 E. HASTRUP 3,462,018,

I DRUM SIEVBS Filed Nov. 5, 1967 2 Sheets-Sheet 1 FIG. I

INVENTOR NIELS E. HASTRUP ATTORNEYS Aug. 19, 1 969 N. E. HASTRUP 3,462,013

DRUM siEvEs 7 Filed Nov. 3. 1967 I 2 Sheets-Sheet 2 FIGS INVENTOR BYR E M 4 ATTORNEYS NIELS E. HASTRUP United States Patent "ice 3,462,018 DRUM SIEVES Niels E. Hastrup, Copenhagen-Valby, Denmark, assignor to F. L. Smidth & Co., New York, N.Y., a corporation of Delaware Filed Nov. 3, 1967, Ser. No. 680,502 Claims priority, application Great Britain, Nov. 8, 1966, 49,939/ 66 Int. Cl. B07b 1/22 U.S. 'Cl. 209-284 6 Claims ABSTRACT OF THE DISCLOSURE A channel is provided at the outlet end of a drum sieve through which tailings must pass before being discharged from the drum. The channel is circumferentially bounded by a sieve for further separation of fines and thus increased capacity and substantially complete separation are realized without increase in length of the drum sieve.

BACKGROUND OF THE INVENTION This invention relates to improvements in drum sieves and more particularly to a channel positioned at the outlet for further separation of fines from tailings.

In continuous screening processes it is common to pass the material to be screened through a cylindrical sieve mounted to rotate about a horizontal axis. Such a sieve may be a drum having an inlet in a wall at one end and open at the other end to allow tailings to be discharged unhindered. Material fed to such a drum builds up at its inlet to some extent, and the depth of the layer of material on the sieve decreases along the bottom of the drum in the direction of travel, with the result that the material extends along the bottom of the drum as a tongue, the tip of which comprises tailings. As the sieve rotates these tailings pass continuously and freely out of the open end of the drum, partly under the influence 0f the pressure of the fresh material fed to the drum. To assist in discharging thhe tailings a stationary scraper is sometimes mounted in the rotating drum.

It is of course important to ensure that no or substantially no particles capable of passing the mesh of the sieve fail to pass through it, and since only a limited area of the sieve is utilized at any given moment the drum must normally be of some minimum length for a given throughput. If it is shorter than this, the separation is incomplete. To increase the length in order to increase the throughput is often not practical. Our object in this invention is to increase the capacity of a sieve drum, and thus to allow the throughput to be increased, without increasing its length.

SUMMARY OF THE INVENTION The invention is in a drum sieve mounted to rotate about a horizontal axis which has a cylindrical wall forming a sieve for separation of fines from material passing therethrough, with a material inlet at one end and an outlet for discharge of tailings at the other end. The improvement is in a channel assembly positioned at the outlet end of the drum to receive tailings and further separate fines. The channel is defined in part by a partition extending across the axis of the sieve drum to block flow of material to the outlet of the drum. A channel is positioned on the drum outlet side of the partition and extends around the axis of the drum and is circumferentially bounded by a sieve. A channel inlet extends through the partition to the channel for introduction of material into the channel as the drum rotates and thereby slide the material over the surface of the sieve in the channel for separation of fines. An outlet from the channel is positioned to receive the sliding tailings and discharge the tailings separate from the fines.

3,462,018 Patented Aug. 19, 1969 The channel is preferably built inside the drum, and the circumferential sieve that bounds it is then part of the cylindrical sieve of the drum. The channel may, however, be outside the drum, the inlet to it then being in the end wall of the drum.

The channel may be open opposite the sieve surface, but is preferably tubular. The inlet to the channel may be in that side of it which faces the inlet of the drum, but is preferably transverse to the channel, so that the tailings are scooped into the channel as the drum rotates. The outlet of the channel is preferably in the side wall remote from the drum inlet, but may be in the sieve surface and coincide with the mouth of a discharge chute.

The channel is most conveniently quadrilateral in crosssection, one side wall being formed by the end wall of the drum.

By means of the invention the depth of the bed of material in the drum at any given moment may be increased, as material can pass out of the drum only through the cylindrical sieve and the discharge channel. Tailings will accumulate at the bottom of the drum against the side wall of the channel, or the end wall of the drum, and when the inlet to the channel reaches the accumulated tailings in the course of the rotation of the drum some of these tailings will pass through it, together with any unseparated fine material, and will rest on the bottom of the channel until the outlet reaches them.

The channel most conveniently extends through a little more than one complete circle, but it may be longer or shorter. It should in any case be constructed so that the tailings cannot pass straight across it from the inlet to the outlet, but rather are forced to slide over its whole length as the drum rotates, and advantageously it is made as at least one full turn of a screw, threaded oppositely to the direction of rotation of the drum.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a vertical longitudinal section through one drum in combination with a tube mill;

FIGS. 2, 3, and 4 are sections taken along the lines 22, 3-3, and 44 respectively in FIG. 1;

FIG. 5 is a vertical longitudinal section through a drum and tube mill showing a second embodiment;

FIG. 6 is a vertical longitudinal section through a drum and tube mill showing a third embodiment; and

FIG. 7 is a section taken along lines 7-7 of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a tube mill 10 carried by two hollow trunnions, one of which, 11, is the outlet for material ground in the mill. A sieve drum 12 is rigidly connected to the trunnion 11 and rotates with the mill 10. This drum comprises a cylindical sieve 13 and end walls 14 and 15, the former having a central inlet opening 16 which registers with the trunnion 11. The drum 12 is mounted inside a casing 17, the greater part of the bottom of which is formed as a hopper 18 for the collection of the fine material that passes through the sieve 13. A partition 19 inside the casing sieve drum 12 embraces near the end wall 15, so as to separate a tailings hopper 20 from the hopper 18. Partition 19 is a ring-shaped or annular member which projects inwardly from the inner surface of the cylindrical portion of the casing 17, the inner edge of this member being disposed in slightly spaced relation to the outer surface of cylindrical sieve 13.

A tubular discharge channel 21 is built inside the drum and is quadrilateral in section, as shown in FIG. 3. This channel is made by fixing a radial wall or annular flow guide member 22 to the inner surface of the sieve 13 along a helical path which extends for over 360, and spanning the wall 22 and the end wall 15 by a cylindrical wall 23.

The other two Walls of the channel are formed by the sieve 13 and (over 360) by the end wall 15. The mouth of the channel is cross-wise with respect to fiow guide 22 and end wall 15. It is shown in FIGS. 2 and 3 as being at right angles to the end wall and forms a tailings inlet 24. At the other end of the channel there is an outlet 25 formed in the end wall 15.

In operation, ground material passes from the mill through the opening 16 and may fill up the drum to the edge of this opening. Most of the fine material passes through the sieve 13. The tailings pass on to the discharge channel 21, and at each rotation of the drum a limited amount of them mixed with material which is fine enough to pass the sieve openings but which so far has not had an opportunity of so passing, is scooped up by the mouth of the channel. During the next rotation of the drum this mixture is thoroughly screened so that after this one rotation only the tailings are left to pass out through the opening 25 and fall into the hopper 20.

In previous sieve drums the end opposite the inlet opening 16 is open, and as the mass of material advances as a tongue through the drum it passes through the sieve and at the end only tailings are left and discharged through the open end, provided that the rate of feed is appropriate. However, if more material is fed to the drum than the sieve is able to handle, part of the fine fraction passes out of the open end together with the tailings. In contrast, the drum according ot the invention can be charged with a greater amount of material than ordinary sieve drums, and as more of the sieve is covered by material more of it is utilized in the screening process. Tailings automatically arrive at the outlet 25 and thus are discharged discontinuously as the drum rotates.

The construction shown in FIG. 5 dilfers from that shown in FIG. 1 only in that its channel 26 is open instead of having the tubular channel 21. The channel is defined by a radial wall partition 22', an extension of sieve 13 and the end wall In FIGS. 6 and 7, an open channel 27 is provided which is cylindrical instead of helical as in FIG. 5, and is bounded on the side nearer to the inlet of the drum by an annular wall portion 28. The inlet is formed by a slot 29 in the wall 28, that is to say, is in the side of the channel. An outlet 30, on the other hand, is in the sieve surface of the channel, and coincides with the mouth of a discharge chute 31.

In the grinding process carried out in the mill only a very small part of the ground product constitutes the tailings in the product leaving the mill through the hollow trunnion. The combination of such a mill with the sieve drum according to the invention is particularly advantageous, as the operation of the sieve is essentially independent of fluctuations in the mill production.

I claim:

1. In a sieve drum mounted to rotate about a horizontal axis and having a cylindrical wall forming a sieve for the continuous separation of fines from material passing therethrough, a casing surrounding said drum having at the bottom a fines discharge hopper and a separate tailings discharge hopper, said drum having an inlet at one end and an outlet and an end wall at the other end, the improvement in combination therewith which comprises a channel assembly at the outlet end of the drum forming a channel for receiving tailings, said channel assembly being defined in part by an annular flow guide projecting inwardly from the interior surface of the sieve drum wall partially blocking the flow of material lengthwise of the drum, a member forming the opposite Wall of said channel, the outside cylindrical wall of said channel being bounded by a portion of the sieve drum, said channel having an inlet crosswise thereof for the introduction of material into the channel as the drum rotates and thereby slides such material over the surface of the channel sieve portion for the separation of fines, an annular partition projecting inwardly near to the drum from the wall of the drum casing and at right angles to the axis of the drum, said channel having an outlet opening for delivering material beyond said partiiion into said tailings discharge hopper at each rotation of the drum.

2. A drum according to claim 1 wherein the channel is circumferentially bounded by part of the sieve of the drum.

3. A drum according to claim 1 in which the inlet to the channel is transverse to it so that the tailings are scooped into the channel as it rotates.

4. A drum according to claim 1 in which the channel is quadrilateral in cross-section, one side wall being formed by the end wall of the drum.

5. A drum according to claim I in which the channel is tubular.

6. A drum according to claim 1 in which the channel is made as at least one full turn of a screw, threaded oppositely to the direction of rotation of the drum and the channel inlet and channel outlet are positioned so that the material will slide along substantially the entire channel.

References Cited UNITED STATES PATENTS 2,451 2/1842 Hort 209297 8,482,270 3/1907 Stanton 209-297 1,387,238 8/1921 Cave 209270 2,307,656 1/1943 Abbott 209-284 X 3,243,041 3/1966 Cowan 209-284 TIM R. MILES, Primary Examiner US. Cl. X.R. 209297 

